Burning unconverted h-oil residual

ABSTRACT

A method of treating a vacuum or atmospheric residuum oil containing sulfur is disclosed in which the residuum is subjected to a high pressure, high temperature hydrocracking and desulfurization evolving hydrogen sulfide (H2S) as a result. Afterward the unconverted residuum is used as fuel in a furnace, evolving sulfur dioxide (SO2) as one of the stack gases. The SO2 in the stack gas is removed and reacted with the H2S evolved during the residuum hydrocracking step to yield elemental sulfur.

United States Patent [191 Mounce [111 3,708,569 1 Jan. 2, 1973 [54]BURNING UNCONVERTED H-OIL RESIDUAL [75] Inventor: William Mounce,Cranbury, NJ.

[73] Assignee: Cities Service Research & Development Company, New York,NY.

22 Filed: Dec. 17,1970

21 Appl. No.: 99,202

[52] US. Cl 423/574, 208/21 l [51] Int. Cl. ..C01d 17/04 [58] Field ofSearch ..23/224, 225; 208/211, 218

[5 6] I References Cited UNITED STATES PATENTS 3,451,923 6/1969 Welty etal. ..208/2ll 3,464,915 9/1969 Paterson et al.... 3,463,611 8/1969l-Iaritatos et al ..23/225 P 2,664,345 12/1963 Kohletal. ..23/225R25,770 4/1965 Johanson ..208/1O Primary Examiner--Oscar R. VertizAssistant ExaminerGeorge O. Peters Attorney-J. Richard Geaman [57]ABSTRACT A .method of treating a vacuum or atmospheric residuum oilcontaining sulfur is disclosed in which the residuum is subjected to ahigh pressure, high temperature hydrocracking and desulfurizationevolving 4 Claims, 1 Drawing Figure 1 BURNING UNCONVERTED H-OIL RESIDUALBACKGROUND OF THE INVENTION This invention relates to a process foreliminating sulfur contamination and emissions in hydrocarbon oils,while producing heat energy. More particularly this invention relates toa process for refining a high sulfur petroleum residuum and eliminatingthe waste gases while obtaining heat generation and free sulfur as aproduct.

It has been necessary for a considerable period to remove sulfur fromthe various products of petroleum oil refining, particularly the lowboiling products such as gasoline and kerosine but also includingrelatively higher boiling fractions such as lubricating oils. In a givenpetroleum crude the concentration of sulfur and other undesirableelements such as nitrogen and oxygen generally increases as boilingpoints of the hydrocarbon constituents of the crude increase. Initialprocessing of the petroleum crude is atmospheric fractionation which maybe followed by vacuum distillation after which the resulting bottomsfraction or residuum contains most of the sulfur.

It is now economically feasible to treat the heavy oil residuum furtherto obtain more desirable products by hydrocracking,hydrodesulfurization, etc. One such hydrocracking process is disclosedby U. S. Pat. No. Re. 25,770, issued Apr. 27, 1965 to Johanson for Gas-Liquid Contacting Process. This and other processes utilize largequantities of hydrogen to treat the heavy residuum at high pressure andtemperature in the presence of a suitable catalyst to yield variousdesirable lower boiling products. A proportion of unconverted residuumremains and contains sulfur bearing compounds. Hydrogen sulfide isgenerally evolved during the hydrocracking of the residuum and isdischarged along with the vapor effluent. The unconverted high sulfurresiduum is unsuitable for many applications and may be employed as acheap fuel. The material presence of sulfur presently precludes its useas a commercial fuel oil due to the necessity of reducing atmosphericpollution. I have, therefore, invented a process for utilizing such highsulfur unconverted residuum together with the hydrogen sulfide evolvedfrom hydrotreating the residuum, to produce both heat energy andelemental sulfur.

SUMMARY OF THE INVENTION My invention is a method for producing freesulfur from a vacuum or atmospheric residuum which contains sulfur. Themethod comprises contacting the residuum with hydrogen in the presenceof a particulate catalyst at high pressure and temperature to convertthe residuum into lower boiling hydrocarbons, evolve H 8 and result in aproportion of unconverted residuum containing sulfur. The unconvertedresiduum is then burned to generate heat and evolve sulfur dioxide,after which the H 8 and S are reacted to produce elemental sulfur.

It is, therefore, an object of my invention to provide a process forproducing elemental sulfur from a residual oil.

Another object of my invention is the production of useful heat energyfrom residual oils containing sulfur.

Yet another object of my invention is to provide a process for reducingatmospheric pollution from sulfur bearing stack gases.

Other objects and advantages of the process of my invention will beapparent from the brief description of the drawings and preferredembodiments which follow.

BRIEF DESCRIPTION OF THE DRAWINGS The process according to the inventionis shown in schematic form in the drawing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawing,vacuum or atmospheric residuum isfed to a vessel 12 together with ahydrogen containing gas. The vessel 12 may be a hydrocracking reactor ofthe type shown in the aforesaid U.S. Pat. No.

Re. 25,770 and is referred to as an H-Oil reactor vessel.

The H-Oil vessel is a high pressure, high temperature reactor, in whicha particulate catalyst bed is maintained. Residuum and the hydrogencontaining gas is fed into the bottom of the vessel 12 through asuitable feed conduit 14. An internal recycle conduit 16 may be mountedvertically in the reactor vessel to allow for recycling of liquid fromthe top portion of the reactor to its bottom in order to obtainsufficient upward fluid velocity through the catalyst bed to expand thebed up to five times its quiescent volume. Such an expanded catalyst bedis referred to herein as an ebullated bed. The resulting expansioncauses random motion of the particulate catalyst with consequenthomogeneity of the catalyst bed and fluid reactants, relatively uniformcatalyst bed temperature and elimination of hot spots and excessivecatalyst coking.

Alternatively, internal recycle of fluids in the reactor vessel may bedispensed with and a much smaller particulate catalyst utilized inconsequence of the reduction of upward superficial velocity of fluids inthe reactor vessel. Thus, where recycling is used the particulatecatalyst may be spherical or elongated extrudates ranging in size fromone thirty-second inch to three-eighths inch, while where no recycle isused the particles may range in size from 200 to 600 microns. Thecatalyst itself may be any suitable natural or synthetic hydrocrackingcatalyst although catalysts compounded of alumina carriers with cobaltand molybdenum cocatalyst are preferred. Temperatures are maintained inthe range of from 650 to 950F, with a temperature of between 800F and850F being preferred. Pressures in excess of 1,000 psig may be used,with a pressure in the range of from 2,000 psig to 3,000 psig beingpreferred.

Feedstock may be any residual oil derived from petroleum oils, shaleoils or tar sands which contain sulfur and at least 25 percent materialboiling above 975F. More particularly high sulfur containing atmosphericand vacuum residuums are the preferred feedstocks. They typically have agravity of less than 20 API at 60F, and initial boiling point above650F, and contain sulfur in excess of 2 percent weight. The hydrogencontaining gas also introduced into the reactor vessel along with thefeedstock is a mixture of light hydrocarbons and recycled and make-uphydrogen. The quantity of hydrogen is on the order of from 2,000 to10,000 standard cubic feet of hydrogen per barrel of feedstock (scf/B)and preferably from 3,000 to 7,000 scf/B.

Effluent is withdrawn overhead from the upper portion of the reactorvessel 12 through an effluent withdrawal line 26 and introduced into aprimary vapor-liquid separator 28. The primary vapor stream is withdrawnoverhead via line 30. Heat exchanger 32 and cooler 33 are mounted inline 30 and serve to transfer heat to the hydrogen containing gas inline 22. The primary vapor stream is subjected, after cooling, to asecond stage vapor-liquid separation in a secondary vapor-liquidseparator 34 to remove any hydrocarbon components which were previouslycondensed. Vapor from the secondary separator 34 is withdrawn overheadthrough line 36, purged and returned to the reactor vessel as hydrogengas. Purging is accomplished by:

use of a flow or pressure regulated valve 37. The purge gas stream iscarried via line 38 to an amine unit 40 where the hydrogen sulfide isseparated out. The hydrogen sulfide then is passed via line 42 to aClause- Type Process unit 44 for conversion to sulfur as will behereinafter described.

Separated liquid from the primary vapor-liquid separator 28 is withdrawnas a stream via line 46 to a secondary separation unit 48. Flow of theliquid stream from the primary separator 28 is controlled by a flowvalve 50 mounted in line 46, which also acts to reduce system pressureto no more than 1,500 psig. Material boiling above 650F is withdrawnfrom the secondary separator 48 via line 52 and passed through athrottling valve 54 to a vacuum tower 56 where the heavy liquid streamis separated into a bottoms stream comprising material boiling above975F and a heavy gas oil stream boiling between 650F and 975F. The heavygas oil is withdrawn as a product stream, but part or all of the gas oilmay be recycled to the reactor vessel via line 24, the latter linehaving pump 58 mounted therein to bring the recycle stream pressure upto reactor unit pressure.

Bottoms from the vacuum tower 56, constituting unconverted residuum andcontaining most of the remaining sulfur, are withdrawn via line 60 to afurnace 62 and burned as fuel for whatever heat generation purpose maybe desired. Stack gases from the furnace which now contain sulfurdioxide pass to a recovery stage 64, utilizing any known process forseparating the from the stack gases. Which produces a substantially pureS0 stream. The sulfur dioxide so removed is passed via line 66 to theunit 44 where it is reacted with the hydrogen sulfide also provided bythe process of this invention to yield elemental sulfur, according tothe following equation:

SO 2H S 38 21-1 0 As is readily apparent, the molar ratio of S0, to H 8is l to 2 for this reaction.

Returning now to the secondary liquid separator 48, the vapor streamprincipally containing materials boiling below 650F is withdrawnoverhead via pipe line 70 cooled in a cooler 72 before being mixed withanother condensed liquid stream and introduced into a third stage gasliquid separator 74. The material boiling below C is separated as vaporfrom the remainder of the stream in the third stage separator 74 andpassed to the gas purge line 38 via connecting line 76. Such a procedureassures substantially total removal of H 8 from the hydrocarbon productstream withdrawn as liquid from the separator 74. The liquid productstream is preferably introduced via line 78 to a fractionation tower 80for separation into products as may be desired.

With a view to further detailing the process according to the presentinvention, the following example is given by way of illustration.

A feedstock comprising 20,000 BPSD (barrels per stream day) of vacuumresidual oil, having an API gravity of 8.5 and 5.28 percent wt. sulfuris introduced into the process described above. Reactor vesselconditions are maintained at 3,000 psig and 840F with 6,000 cubic feetof hydrogen per barrel being used. The hydrogen sulfide being producedas a result of hydrocracking and hydrodesulfurization amounts to 6,870lbs mole per day. Burning of the unconverted fraction of materialboiling above 975F yields about 3,620 lbs mole per day of sulfurdioxide. Product yield of the hydrocracking operation in the reactor isas listed below.

% Weight BPSD Sulfur c1-c3 2.71 04-400? 11.41 3400 0.1 400-650F 21.125040 0.5 650-975F 29.16 6360 1.4 97s1=+ 33.44 6020 4.9 Totals: 101.4820,820 1.9

With percent recovery of S0 in the stack gas recovery process, thisrepresents 3,260 lbs mole per day of recovered S0 With percent removalof H 8 in removal amine scrubbing process, this represents 6,530 lbsmoles per day of recovered H 8. The operating conditions and thecatalyst activity in the hydrocracking reactor are controlled such thatthere is sufficient sulfur left in the unconverted 975F plus materialsuch that the S0 recovered after combustion of this 975F plus oil isjust sufficient to react with the H 8 recovered since the S0 to H 8molar ratio is 1:2.

It can be seen that sulfur content of the final product fractions ismeasurably reduced. The unconverted residuum which contains most of theremaining sulfur is burned and the resulting SO, used as feed for aClaus type unit as a source of 80,.

Having described the process of my invention and wishing to cover thosemodifications and variations which would be apparent to those skilled inthe art without departing from the spirit and scope thereof, I claim:

1. A process for producing sulfur from a residual oil containing sulfur,said method comprising a. contacting said residual oil with hydrogen inthe presence of a particulate catalyst at high pressure and hightemperature to desulfurize and convert said residual oil into lowerboiling hydrocarbons, and resulting in the production of H 8 and a heavyoil fraction containing sulfur,

b. separating said converted desulfurized lower boiling hydrocarbons,said heavy oil and said H 8 into different streams,

c. burning said heavy oil as fuel, said burning resulting in theproduction of S0 and heat, and

d. reacting said S0 and H s to produce elemental sulfur and water.

2. The process of claim 1 wherein said step of contacting said residualoil with hydrogen comprises passing said residual oil and a hydrogencontaining gas upwardly through a particulate catalyst bed at asuperficial upward velocity sufl'icient to expand said catalyst bed upto five times the initial volume in a reaction" zone maintained underconditions of pressure between about 1,500 psig and 3,000 psig andtemperature between about 800F and 900F.

3. The process of claim 2 wherein said step of separating said converteddesulfurized lower boiling hydrocarbon oil, heavy oil and H s compriseswithdrawing a liquid stream from said reaction zone,

separating said liquid stream into a said heavy oil fraction boilingabove 975F, and into a lower boiling hydrocarbon fraction fractionatingsaid lower boiling hydrocarbon fraction

2. The process of claim 1 wherein said step of contacting said residualoil with hydrogen comprises passing said residual oil and a hydrogencontaining gas upwardly through a particulate catalyst bed at asuperficial upward velocity sufficient to expand said catalyst bed up tofive times the initial volume in a reaction zone maintained underconditions of pressure between about 1,500 psig and 3,000 psig andtemperature between about 800*F and 900*F.
 3. The process of claim 2wherein said step of separating said converted desulfurized lowerboiling hydrocarbon oil, heavy oil and H2S comprises withdrawing aliquid stream from said reaction zone, separating said liquid streaminto a said heavy oil fraction boiling above 975*F, and into a lowerboiling hydrocarbon fraction fractionating said lower boilinghydrocarbon fraction into a gas-oil fraction containing sulfur bearingmaterial and into said desulfurized lower boiling hydrocarbon oil, andrecycling said gas-oil fraction to said contacting zone.
 4. The processof claim 1 in which the residual oil of step (a) is contacted withhydrogen under controlled operating conditions such that when the heavyoil fraction of step (a) is burned as fuel in step (c), the SO2 formedin the burning is just sufficient to react with the H2S produced in step(a) in the molar ratio of 1:2.